Crop dehydrator

ABSTRACT

A dehydrator including an elongated drum mounted for rotation about its longitudinal axis. A frustoconical furnace sidewall cooperates with a ring burner to provide hot combustion gases for dehydrating material in the drum. Vanes in the drum are bent at varying angles to enhance even distribution of the material across the drum and cleats are also provided to reduce the slippage of material from some of the vanes.

United States Patent [72] Inventor Stanley P. Thompson Box 7, St. Marys,Kans. 66536 [21] Appl. No. 773,188 [22] Filed Nov. 4, 1968 [45] PatentedJuly 20,1971

[54] CROP DEHYDRATOR 8 Claims, 9 Drawing Figs.

[52] US. Cl 114/108, 263/33 [51] Int. Cl F26b 11/02 [50] Field of Search34/109, 124,125, 137,431/37, 89; 263/19 A, 33; 236/15 C [56] ReferencesCited v UNITED STATES PATENTS 263,584 8/1882 Rice 34/137 1,154,2079/1915 Roberts.... 263/15 1,987,242 l/1935 Madsen.... 34/137 2,292,2438/1942 Schwartz 236/15 Primary Examiner Frederick L. Matteson AssistantExaminerTheophil W. Streule Attorney-Don M. Bradley ABSTRACT: Adehydrator including an elongated drum mounted for rotation about itslongitudinal axis. A frustoconical furnace sidewall cooperates with aring burner to provide hot combustion gases for dehydrating material inthe drum. Vanes in the drum are bent at varying angles to enhance evendistribution of the material across the drum and cleats are alsoprovided to reduce the slippage of material from some of the vanes.

I PATENTEU JULZO I971 SHEEI 1 OF 2 A ORNEYfi CROP DEHYDRATOR Thisinvention relates to material-processing apparatus and, moreparticularly, to a dehydrator for hay and other products.

It is a very important object of this invention to provide a dehydratorhaving a furnace equipped with a combustion chamber of novel shape forenhancing the transfer of heat into the dehydrator drum and forminimizing deleterious effects from the heat on the furnace wall.

Still another object of this invention is to provide a dehydratorfurnace having improved gas flow characteristics in that expansion ofgases resulting from combustion is accommodated by a progressivelyenlarged combustion chamber in the direction of flow of the gases.

A further object of the invention is to provide a dehydrator furnacemaking maximum use for the preheating of air, of heat which wouldotherwise be lost from the system. In this connection, it is alsoanobject of the invention to provide novel structure for creatingairflow patterns calculated to produce enhanced combustion uponintroduction of air into the furnace.

In the achievement of the foregoing objects, it is also an object of theinvention to provide a novel dehydrator furnace combining a ring burnerwith a conical-combustion chamber to derive increased efficiency anduniformity in operation of the dehydrator system.

Still another very important object of this invention is the provisionof a dehydrator having flights of vanes strategically positioned andshaped to distribute the material as uniformly as. possible across theentire cross section of the drum to cause maximum transfer of heat fromthe hot gases of combustion to the material as the latter travelsthrough the rotating drum.

ln carrying out the preceding object, it isalso another object of theinvention to provide vanes configured to permit automatic separation ofrelatively light or leafy material from heavier or stemmy material sothat the lighter particles may be carried out. of' the drum by theairstream in advance of the heavier particles which require further timein' the drum to achieve a uniformly dried product.

A. yetfurther object of this invention is the provision of a novelcontrol for the dehydrator furnace fuel supply so that the output of thefurnace may be controlled by the operator at the inlet end of thesystem, even though the fuel supply is coupled through a controller forautomatic adjustment responsive to heat requirements-sensed at the.outlet end of the dehydra tor drum.

Another object of this invention is the provision of an annular flameretainer provided in the refractory lining of the combustion chamber toinsure stabilization of the flame from the ring burner and also tominimize-the level of the noise resulting from operation of the system.

These and other important objects of the invention will be furtherexplained or will be apparent from the drawings, specification andclaims.

In-thedrawings:

FIG. 1 is afragmentary, side elevational viewon aireduced scale andpartially schematic of a dehydrator system incorporating the principlesof this invention, parts being broken away and appearing incross sectionto reveal details of construction;

FIG., 2 is a vertical, cross-sectional view through the dehydrator drumtransversely thereof;

FIG. 3 is a fragmentary, vertical, cross-sectional view through the drumlongitudinally thereof, the flighting appearing in elevation;

FIG. 4-is a vertical, cross-sectional view through the furnace, the airblowerappearing in elevation;

FIG. 4a is an enlarged, detailed view of a portion of FIG. 4 showing themounting of the ring burner in the furnace and illustrating the annularflame retainer'in the refractory lining of the combustion chamber;

FIG. S-is a vertical, cross-sectionalview taken along line 5-5 of F IG;4;

FIG. 6 is an enlarged, fragmentary front elevational view of the ringburner;

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. I; and

FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 7.

Referring initially to FIG. 1' of the drawings, the dehydrator of thisinvention includes an elongated, cylindrical drum 10 having a sidewall12 and an outlet end wall 14. A furnace l6 communicates with the inletend of drum 10 and a fan broadly designated 18 is interposed in amaterial discharge conduit 20 which communicates with the outlet end ofdrum 10 through a discharge opening 22 best seen in FIG. 7. A materialinlet conveyor 24 is provided adjacent furnace 16 at the inlet end ofdrum 10 for the purpose of introducing the material to be dehydratedinto the drum. The latter is mounted for rotation about its longitudinalaxis on roller means 26 and is powered by drive means (not shown) toeffect rotation of the drum in the direction of the arrow in FIG. 2.

Furnace 16 includes a blower 28 for providing air to be mixed with thefuel which is introduced into furnace 16 through a fuel line 30. The hotgases of combustion are directed into the interior of drum 10 for dryingthe material as the latter progresses through the drum. To this end,blower or fan 18 serves to draw the gases through the drum so that thedried material is drawn toward outlet opening 22 and into conduit 20. Itwill be understood that conduit 20 may communicate with a cycloneseparator or the like (not shown) so that the dehydrated material may beseparated from the airstream for further processing as may be desireableor required.

In the drying of hay or other materials it is particularly importantthat as much surface area of the material particles as possible beexposed to the drying influence of the hot gases passing through thedrum. To this end, the interior of drum I0 is provided throughout itslength with a flighting adapted to engage the material upon rotation ofthe drum and to distribute" the material as uniformly as possible acrossthe entire hollow cross section of the drum. Manifestly, upon lifting ofthe material to a given position as the drum rotates, the material isdropped for gravitation toward the bottom of the drum. The material isthereupon again lifted by the flighting for subsequent distribution topermit gravitation of the particles of material through the hot streamof gases and toward the bottom of the drum whereupon the processcontinues successively until the material is sufficiently dehydrated tobe carried to the discharge end of the drum by the hot gases.

The flighting to accomplish the foregoing operation on the material inthe drum includes a plurality of vanes secured in annular rows to theinner surface of the cylindrical drum wall 12. Each row of vanesincludes a series of differently shaped vanes. Thus, a vane 32 comprisesa substantially flat panel 34 having one end thereof secured as bywelding or the like to the inner surface of wall l2. The panel 34extends radially inwardly of the drum and terminates in a lip 36 at themarginal edge of panel 34' remote from wall 12.

The next successive vane 38 in the row proceeding in a counterclockwisedirection is spaced circumferentially from vane 32 and comprises a panel40 having one marginal edge thereof secured as by welding or the like tothe inner surface of sidewall 12 similar to the attachment of panel 34to the drum. It should be-noted, however, that the panel 40 is providedwith a line of bend 42 in spaced relationship from wall 12 and from theinnermost end of the panel. Thus, the panel comprises a portionextending radially inwardly of the drum and a second portion deviates atan angle from the direction of the first portion as illustrated clearlyin'FlG. 2. The outermost end of panel 40 is provided with a lip 44similar to lip 36 of panel 34.

The next successive vane 46 of the series of vanes is similar to vane 38in that it is provided with a line of bend 48 intermediate its ends.However, the angle of bend of the portions of the vane 46 is such thatthe vane is straighter than vane 38. Again, vane 46 is provided with alip 50 at its innermost end.

Although the specific arrangement of the different vanes in the seriesdepicted has been found desirable, other arrangements for the vanes willalso produce advantageous results.

Referring to FIGS. 2 and 3, it may be seen that each row 52 of vanes maybe identical to the adjacent rows but it has been found to be desirablethat each successive row longitudinally of the drum be rotated withrespect to the preceding row. Thus, a vane 32 is not directly adjacentan identical vane 32 of the adjacent row. Rather, it is adjacent a vane38 or a vane 46. Similarly, the vanes 42 and 46 are disposed besidedissimilar vanes of the adjacent row.

Certain of the vanes are provided intermediate their lengths with cleats54 which may be formed of key stock material welded to the leadingsurface of the vane. The cleats 54 serve to retard the slippage of thematerial along the surface of the vane for a purpose to be more fullyexplained hereinafter.

A longitudinally extending shaft 56 is disposed axially of drum and issecured to the latter by a plurality of hangers 58. Each hanger 58includes an arcuate portion 60 having one end thereof secured to theouter surface of shaft 56 by welding or the like and an integralstraight portion 62 having its outermost end with to the inner surfaceof drum 10. It will be understood that as many hangers 58 are providedas are necessary for securing the shaft in its proper position. Further,the provision of the arcuate portion 60 disposed in a wrappedaroundmanner adjacent the outer surface of shaft 56 insures that the latter ismaintained in its proper axial position even when the hangers 58 andshaft 56 are exposed to the extreme temperatures caused in drum 10 bythe hot dehydrating gases provided by furnace 16. It should be notedthat the straight portions 62 of hangers 58 extend tangentially of shaft56 so that heating of the hangers 58 merely causes a rotation of shafts56 without moving the latter from its axial position.

Shaft 56 mounts a plurality of vanes 64 extending radially outwardlyfrom the shaft. The vanes 64 are connected with brace members 66 asillustrated best in FIG. 2. Further, each vane 64 is provided with acleat 68 on its leading and its trailing surface to reduce the slippageof material on the vane. Shaft 56 rotates with the drum 10 therebyrotating the vanes 64.

Referring now particularly to FIGS. 1 and 4--6, furnace 16 includes afrustoconical, tubular sidewall 70 provided with a liner 72 ofrefractory material defining a frustoconical combustion chamber 74. Thelatter is provided with an annular offset 76 adjacent its smaller, inletend presenting an annular shoulder 78. Liner 72 is preferably cast foreconomy of fabrication. A plurality of hanger elements 80 extending intomaterial 72 serve to mount an annular, tubular ring-type burner 82 inconcentric relationship with the inlet opening of the combustion chamber74 as illustrated in FIGS. 4 and 4a. The inlet end of the furnace isclosed by a plate 84 having a circular opening 86 axially aligned withthe combustion chamber 74. The fuel line 30 communicates with the ringburner 82 and the latter is provided with a plurality of spaced orifices88 as illustrated best in FIG. 6.

A jacket or shroud 90 circumscribes wall 70 of furnace 16 throughout asubstantial portion of the length thereof and is mounted in outwardlyspaced concentric relationship therewith by spacers 92 spanning thedistance between jacket 90 and wall 70. A conduit 94 extends generallytangentially to jacket 90 and is in communication therewith and withblower 28. The outlet side of the latter is in communication with aclosed circular vessel 96 having an annular sidewall 98 and end walls100, one of the latter having an opening 102 aligned with opening 86 inthe furnace end wall 84. The communication between the blower 28 andvessel 96 is through an inlet 104 which extends tangentially of thesidewall 98 of vessel 96 as illustrated in FIGS. 4 and 5.

A control for the supply of fuel to furnace 16 includes a line 106 whichis adapted to be coupled with a source of pressurized fluid such as themain fuel line 30. Line 106 is equipped with a pressure regulator 108and a micrometer flow control valve 110. Line 106 communicates with acontrol line 112 which, in turn, flows through a temperature responsiveflow controller 114. The latter has a temperature-sensing element 116extending into the discharge conduit 20 at the outlet end ofdrum 10 asillustrated in FIG. 1. Thus, element 116 senses the temperature of thehot gases as the latter discharge through conduit 20. Element 116 thenoperates controller 114 to adjust the pressure flowing through line 112responsive to the temperature of the gases in conduit 20.

Line 1 12 is also operably connected with the diaphragm ofa throttlingvalve 118 interposed in the main fuel supply 30 upstream of the ringburner 82. Valve 118 is constructed so that the valve settingcontrolling the flow of fuel through line 30 is manually adjustable eventhough the valve setting is responsive to the pressure in line 112. Inother words, the particular setting of valve 118 governing the flow offuel through line 30 corresponding with a particular pressure of fluidin line 112 may be manually regulated or varied.

In operation, fuel emanating from the orifices 88 in ring burner 82 isignited in the combustion chamber 74. Drum 10 is powered to rotate onits longitudinal axis and blower 28 is operated to provide air to thefurnace as is necessary for proper combustion of the fuel in thecombustion chamber. The fan or blower 18 is also operated to insure aflow of gases longitudinally through drum 10 from the inlet end thereofto the discharge so that the dehydrated material which enters drum 10through conveyor 24 moves progressively through the drum and outdischarge conduit 20. The shoulder 78 near the burner 82 serves as aflame retainer by virtue of the turbulence and reduction of velocity inthe combustible mixture as the same traverses through the combustionchamber from left to right as viewed in FIG. 4. Accordingly, a generallyannular ring of flame or combustion proceeds from ofiset 76 in thedirection of enlargement of the combustion chamber. The taper of thecombustion chamber accommodates the increase in volume of the gases fromcombustion as they progress through the combustion chamber so that thegases flow through the furnace at a relatively uniform velocity despitesuch volume increase. A portion of the heat from combustion travelsthrough the furnace wall and serves to preheat the air for combustionwhich enters the annular orifice defined by the mouth of the shroud orjacket proximal the outlet end of the furnace. Since the inlet to blower28 extends substantially tangentially to the annular chamber defined bythe wall 70 and jacket 90, the air tends to follow a generally swirlingpath of travel around wall 70 on its way to the blower. This insuresmaximum possible heat interchange between the air and the furnace wall70 to preheat the air for increasing the efficiency of operation of thesystem. Further, the air which is discharged by blower 28 travels in acircular pattern in vessel 96 to enter the combustion chamber in aspiraling or swirling motion as it travels through the aligned openings102 and 86 adjacent ring burner 82.

This spiraling and swirling motion increases the turbulence of the airas the latter combines with the fuel emanating from the orifices 88 inburner 82 to enhance the mixing of fuel and preheated air for greatercombustion efficiency.

Shoulder 78 tends to hold the flame in its proper position within thecombustion chamber to eliminate the noise attendant upon a vacillatingor transitory flame location and also to prevent the flame from becomingextinguished during variations in the fuel flow through the burner.

The taper of the inner surface of the combustion chamber in thedirection shown tends to reflect a component of the heat of combustiontoward the drum entrance. This has the twofold advantage of transferringthe heat in the direction where it is desired for dehydrating thematerial in the drum and also for reducing the possibility of burnout ofthe combustion chamber lining. The latter permits the economy ofoperation of furnace 16 with a substantially thinner lining than wouldotherwise be possible.

The rotating drum constantly moves the vanes in a counterclockwisedirection as viewed in FIG. 2 so that the material in the drum is pickedup by the vanes as they rotate along their lowermost positions withinthe drum. The material is retained on the vanes as the same is liftedthereby until the v'ane reaches a position along its path of travelwhere the vane drops the material for gravitation across the drum towardthe bottom of the drum. The different shapes of the fingers insure thatthe material release point for the various fingers is reached atdifferent positions of rotation of the drum. Thus, a substantiallyuniform curtain of material in relatively small clumps is alternatelypicked up and then released by the successive fingers for gravitationacross the drum.

The central vanes 64, however, prevent the material from gravitating tothe bottom of the drum when it is first dropped by the vanes 32, 38 and46. The vanes 64 retard the travel of the material to the bottom of thedrum by catching the material at an intermediate point along its path oftravel. After the material is caught by the vanes 64, the latter carrythe material over for subsequent release to gravitate to the bottom ofdrum 10. This subsequent release of the material occurs at a point intime subsequent to the release of the material by the correspondingvanes 32, 38 and 46. The shortened paths of gravitation of the materialinsures that the gas flow through the drum does not have sufficient timeto act on the material while falling to move the material through thedrum at too fast a rate for proper drying.

The cleats 54 and 68 on the respective vanes further tend to dribble thematerial from the vanes rather than releasing the same in a clump whenthe vane reaches a position for discharging material. This also servesto enhance the distribution of the material uniformly across the drumfor maximum exposure of the material to the hot gases of combustion fordehydrating the material.

Not to be overlooked is the effect of the rows of vanes which aredisposed in series and in offset relationship longitudinally of thedrum. This arrangement for the vanes which are secured to the innersurface of the cylindrical sidewall 12 re tards against the materialfrom bunching as the material moves longitudinally through the drum.

Referring now particularly to FIGS. 1, 7 and 8, it may be seen that theend wall 14 at the discharge end of the drum is provided with aplurality of inwardly extending, radially disposed members 120 havinglips 122 extending along the innermost marginal edges thereof and in thedirection of advancement of the drum during operation. The members 120terminate at the peripheral margin of opening 22 in wall 14. The members120 and their respective lips 122 thus serve as positive dischargescoops which tend to receive the dehydrated material and to conduct thesame toward the discharge opening 22. it has been found desirable toprovide cleats 124 intermediate the ends of the members 120, again todribble the material toward the outlet opening 22 rather than to permitthe material to slide as a bunch toward the outlet opening when theposition of the member is reached which would otherwise permit slippageof the material by gravity along the member.

Controller 114 may be ofa type which produces an increase in thepressure of fluid in line 112 responsive to the sensing by element 116of a reduction of the temperature in conduit 20 below a predetermineddesired temperature. The increase of pressure in line 112 acts upon thediaphragm of valve 118 to cause the valve member of the latter to moveto a position to increase the flow of fuel to the burner. This resultsin an increase in the heat output of the furnace to raise thetemperature in the system. Controller 114 and line 112 operate tomaintain the temperature in the system correlated to the load on thesystem or amount and kind of material passing through the drum. It willbe understood that line 112 may exhaust to atmosphere after passingthrough controller 114 as is conventional in fluid control systems ofthe type described.

A decrease of the pressure in line 112 responsive to a temperature inconduit 20 above that required for the particular load on the systemwill have the opposite effect causing a diminution in the fuel supply tothereby lower the temperature emanating from furnace 16.

Manually adjustable valve 118 provides the advantage of normallyautomatic operation of the system under the control of the temperatureresponsive controller 114. However, when it is desired to alter thetemperature of operation of the system it is not necessary to readjustor to replace the controller 114. The dehydrator operator quickly andeasily accomplishes this by manually adjusting valve 118 to increase ordecrease the flow of fuel to the burner. Manifestly, any manualadjustment of valve 118 merely changes the reference point from whichcontroller 114 continues to automatically monitor and regulate the flowof fuel to the system.

The automatic monitoring of this system is extremely important. Theresponse of the heat output from the furnace to changes in heatrequirements is much faster than is possible with systems provided withmanual controls. Changes in the heat of operation of the system areinversely proportional to the changes in fuel supply to the burner. Thatis to say, the closer the fuel supply follows the heat requirementsdictated by the load, the more uniform will be the temperature ofoperation of the system.

The nature of the material handled by a dehydrator system of this typedictates that the load on the system will not be uniform. For example,the material may be bunched, will vary in moisture content, and mayfluctuate radically in the proportion of leafy or fine materialcomprising the load. Accordingly, the operating temperature in thesystem will necessarily vary upwardly and downwardly from a selectedoperating mean temperature. The amplitudes of such inevitable variationsare kept relatively small in the system of this invention, however,since the remedial changes in heat input from the furnace closely followthe load variations.

Referring now to FIG. 1, it may be seen that the system includes adamper 126 in the outlet of blower 28 and controlled by a gas-operatedactuator 128 which is operably coupled with the fuel line 30 by a line130. Another damper 132 is interposed in the outlet of fan 18. Anactuator 134 is coupled to line 30 by a conduit 136 (shown butfragmentarily in FIG. 1). Actuator 132 is similar to actuator 128, butis of the delay type so that it operates damper 132 only after a delayof a predetermined time interval following a change of pressure inconduit 136.

Actuator 128 is proportioned to maintain the proper setting for damper126 to provide the correct amount of air to furnace 16 at all times.Thus, as the fuel flow in line 30 increases or decreases, damper 126 isopened or closed to provide the correct amount of air for maximumcombustion of the fuel in the furnace.

Damper 132 at the outlet end of the dehydrator also is moved in responseto changes in the flow of fuel in line 30. The greater the fuel flow,the wider damper 132 is opened by actuator 134. This permits a fasterflow of the gases through the dehydrator drum to pneumatically conveythe particles of material through the dehydrator at a faster rate.

Conversely, when the flow of fuel gas in line 30 is lessened as the heatrequirements for the load in the system diminish, damper 132 is movedtoward a closed position to reduce the rate at which the material isconveyed by the gases through the drum.

Actuator 134 is constructed so that it operates in response to changesin the fuel pressure in line 30. This insures that the rate at which thematerial is conveyed through the system does not change immediately uponthe sensing of a change in the heat required for the load. Rather, therate of movement of the material occurs after furnace 16 has had anopportunity to adjust its heat output to accommodate the load changes.This means that the material movement rate is correlated to the furnaceheat output and contributes to the production of a uniformly driedproduct from the system.

I claim:

1. In a dehydrator including an elongated drum having a material inletat one end of the drum and an outlet at the other end thereof, and meansmounting the drum for rotation about its longitudinal axis, thecombination with said drum of a furnace for providing hot gases to thedrum, said furnace comprising:

a frustoconical, tubular combustion chamber communicating with the inletend of the drum, said chamber being disposed with the end thereof havingthe greatest diameter adjacent said drum inlet; and

a ring burner in the combustion chamber at the end thereof remote fromsaid drum inlet,

the sidewall of said chamber having a uniform, substantially continuoustaper in a direction toward the drum inlet to reflect a portion of theheat from said combustion out of the chamber and into the drum throughsaid inlet.

2. The invention of claim 1, wherein said burner includes an elongatedtube shaped into a ring, the axis of said ring being in generalalignment with the longitudinal axis of said combustion chamber, and aplurality of ports in the tube for egress of fuel for combustion.

3. The invention of claim 2, wherein is provided an annular offset inthe inner surface of said sidewall downstream of said burner forretaining the zone of initiation of the flame of said combustion in theregion of said annular offset during operation of said furnace means.

4. The invention of claim 1, wherein is included inlet means forproviding air to said combustion chamber, said air inlet means includinga tubular shroud extending around the sidewall of said chamber inoutwardly spaced relationship from the latter and communicating with thechamber, the inlet end of said shroud being remote from the zone ofcommunication between the shroud and the chamber whereby heat emanatingthrough the sidewall may preheat the air traveling through the shroud.

5. The invention of claim 4, wherein said air inlet means includes aclosed vessel having a pair of spaced-apart end walls and an annularsidewall, there being an opening in one of said end walls communicatingthe vessel with the chamber, and conduit means extending between theshroud and the vessel and including an inlet for the vessel extendingtangentially to said annular sidewall to impart a swirling of the air inthe vessel to enhance turbulence of the air as the latter enters thecombustion chamber.

6. The invention of claim 5, wherein is provided blower means interposedin said conduit means, and wherein is provided a discharge for said airfrom the shroud and upstream of the blower means, said dischargeextending generally tangentially from said shroud to enhance theswirling of the air around the sidewall of the combustion chamber as theair is drawn through the shroud.

7. In a dehydrator including an elongated drum having an inlet end andan outlet, a furnace for providing hot gases to the inlet end of saiddrum, said furnace including an inlet damper means interposed in thefurnace air supply structure, and a fuel supply line coupled with thefurnace and adapted to be coupled with a source of fuel under pressure,a control for said dehydrator comprising:

a conduit in fluid communication with said supply line and vented toatmosphere;

temperature controlled valve means interposed in said conduit andincluding temperature responsive actuator means for the valve means anddisposed to control the valve means for regulating the fluid pressure inthe conduitresponsive to the temperature at the outlet end of said drum;

a valve interposed in said fuel supply line for regulating the flow offuel to the furnace;

means responsive to the pressure of fluid in the conduit and operablycoupled with said valve and with the inlet damper means forautomatically operating the valve and inlet damper to regulate the fueland air supply responsive to the temperature at said outlet end,

fan means operably coupled with the outlet end of said drum for creatingartificial currents of gases through the drum to convey the material tosaid outlet;

outlet damper means operably associated with the fan means forregulating the velocit of said currents; and actuator means operablycouple with the outlet damper means and said fuel supply line andresponsive to the fuel flow in the latter to automatically regulate saidoutlet damper to control the rate of conveying of the material throughthe drum responsive to the fuel supply to said furnace, said actuatormeans including time delay means to permit movement of said outletdamper means only after a predetermined time increment following achange in the flow of fuel through said line, whereby to effect uniformdrying of the product.

8. In a furnace for use in providing a stream of combustion gases,structure for providing air for combustion to the chamber, saidstructure comprising:

a closed, cylindrical vessel having a pair of spaced apart end walls andan annular sidewall, the vessel being disposed at the inlet end of saidchamber, there being an opening in the endwall adjacent the chambercommunicating the vessel with the chamber;

a tubular shroud extending around the sidewall of the chamber inoutwardly spaced relationship from the latter and having an outletopening through the shroud at the end thereof proximal the vessel, thespacing between the shroud and the outer surface of the chamberpermitting flow of air between said chamber surface and the shroud topreheat the air;

a discharge conduit communicating with the shroud opening and extendinggenerally tangentially outwardly therefrom;

inlet structure for the vessel including an inlet conduit extendinggenerally tangentially from the annular sidewall and communicatingtherethrough; and

blower means interposed between the discharge and inlet conduits wherebyair is drawn in a swirling path around the chamber and is discharged ina swirling path into the vessel for swirling flow through the openinginto the combustion chamber.

1. In a dehydrator including an elongated drum having a material inletat one end of the drum and an outlet at the other end thereof, and meansmounting the drum for rotation about its longitudinal axis, thecombination with said drum of a furnace for providing hot gases to thedrum, said furnace comprising: a frustoconical, tubular combustionchamber communicating with the inlet end of the drum, said chamber beingdisposed with the end thereof having the greatest diameter adjacent saiddrum inlet; and a ring burner in the combustion chamber at the endthereof remote from said drum inlet, the sidewall of said chamber havinga uniform, substantially continuous taper in a direction toward the druminlet to reflect a portion of the heat from said combustion out of thechamber and into the drum through said inlet.
 2. The invention of claim1, wherein said burner includes an elongated tube shaped into a ring,the axis of said ring being in general alignment with the longitudinalaxis of said combustion chamber, and a plurality of ports in the tubefor egress of fuel for combustion.
 3. The invention of claim 2, whereinis provided an annular offset in the inner surface of said sidewalldownstream of said burner for retaining the zone of initiation of theflame of said combustion in the region of said annular offset duringoperation of said furnace means.
 4. The invention of claim 1, wherein isincluded inlet means for providing air to said combustion chamber, saidair inlet means including a tubular shroud extending around the sidewallof said chamber in outwardly spaced relationship from the latter andcommunicating with the chamber, the inlet end of said shroud beingremote from the zone of communication between the shroud and the chamberwhereby heat emanating through the sidewall may preheat the airtraveling through the shroud.
 5. The invention of claim 4, wherein saidair inlet means includes a Closed vessel having a pair of spaced-apartend walls and an annular sidewall, there being an opening in one of saidend walls communicating the vessel with the chamber, and conduit meansextending between the shroud and the vessel and including an inlet forthe vessel extending tangentially to said annular sidewall to impart aswirling of the air in the vessel to enhance turbulence of the air asthe latter enters the combustion chamber.
 6. The invention of claim 5,wherein is provided blower means interposed in said conduit means, andwherein is provided a discharge for said air from the shroud andupstream of the blower means, said discharge extending generallytangentially from said shroud to enhance the swirling of the air aroundthe sidewall of the combustion chamber as the air is drawn through theshroud.
 7. In a dehydrator including an elongated drum having an inletend and an outlet, a furnace for providing hot gases to the inlet end ofsaid drum, said furnace including an inlet damper means interposed inthe furnace air supply structure, and a fuel supply line coupled withthe furnace and adapted to be coupled with a source of fuel underpressure, a control for said dehydrator comprising: a conduit in fluidcommunication with said supply line and vented to atmosphere;temperature controlled valve means interposed in said conduit andincluding temperature responsive actuator means for the valve means anddisposed to control the valve means for regulating the fluid pressure inthe conduit responsive to the temperature at the outlet end of saiddrum; a valve interposed in said fuel supply line for regulating theflow of fuel to the furnace; means responsive to the pressure of fluidin the conduit and operably coupled with said valve and with the inletdamper means for automatically operating the valve and inlet damper toregulate the fuel and air supply responsive to the temperature at saidoutlet end, fan means operably coupled with the outlet end of said drumfor creating artificial currents of gases through the drum to convey thematerial to said outlet; outlet damper means operably associated withthe fan means for regulating the velocity of said currents; and actuatormeans operably coupled with the outlet damper means and said fuel supplyline and responsive to the fuel flow in the latter to automaticallyregulate said outlet damper to control the rate of conveying of thematerial through the drum responsive to the fuel supply to said furnace,said actuator means including time delay means to permit movement ofsaid outlet damper means only after a predetermined time incrementfollowing a change in the flow of fuel through said line, whereby toeffect uniform drying of the product.
 8. In a furnace for use inproviding a stream of combustion gases, structure for providing air forcombustion to the chamber, said structure comprising: a closed,cylindrical vessel having a pair of spaced apart end walls and anannular sidewall, the vessel being disposed at the inlet end of saidchamber, there being an opening in the endwall adjacent the chambercommunicating the vessel with the chamber; a tubular shroud extendingaround the sidewall of the chamber in outwardly spaced relationship fromthe latter and having an outlet opening through the shroud at the endthereof proximal the vessel, the spacing between the shroud and theouter surface of the chamber permitting flow of air between said chambersurface and the shroud to preheat the air; a discharge conduitcommunicating with the shroud opening and extending generallytangentially outwardly therefrom; inlet structure for the vesselincluding an inlet conduit extending generally tangentially from theannular sidewall and communicating therethrough; and blower meansinterposed between the discharge and inlet conduits whereby air is drawnin a swirling path around the chamber and is discharged in a swirlingpath into the vessel for swirling flow through thE opening into thecombustion chamber.